Copper tolerance in the lichen photobiont Trebouxia erici (Chlorophyta)

A copper-tolerant strain of Trebouxia erici was obtained from axenic culture (UTEX 911) by increasing the copper concentration of the medium up to 4 mM. On three different copper-containing media analysis showed significantly higher growth inhibition of the wild strain than of a strain surviving 3 years of copper exposure, strongly supporting the hypothesis that tolerance was developed by selection. Differences between strains were observed in cell dimensions after copper exposure, as well as in the relative number of plasmolysed cells. Copper also altered the chlorophyll content of both strains, causing a significant decrease of chlorophyll a and chlorophyll a+b concentrations, as well as the chlorophyll a/ b ratio and level of chlorophyll degradation. However, the effect on wild type was significantly greater. Co-tolerance to zinc, mercury, cadmium and cobalt was not observed.